Cerebrovascular disorders such as cerebral infarction and cerebral hemorrhage, and diseases that strongly affect higher brain functions such as Alzheimer's disease exhibit poor prognosis, and bring decreased QOL (Quality of Life) on elderly people and further psychological stress on caretakers. Several pharmaceutical agents for improving brain functions have been developed and marketed to date. However, a sufficient therapeutic effect has not yet been obtained by using any of them. Thus, new and more effective agents for improving brain functions and agents for preserving brain functions are expected to be developed rapidly.
Meanwhile, N-methyl-D-aspartic acid (hereafter referred to as “NMDA”) receptor, which is one kind of receptor for glutamic acid that is an excitatory neurotransmitter, is known to transport Ca2+ to neuron and thereby strongly participate in memory formation and in development of symptoms in cerebral ischemia.
The present inventors already reported in the Non-Patent Document 1 shown below that NMDA receptors expressed on Xenopus oocytes followed by contacting with a plurality of polyamine derivatives and measuring a change in electric potential resulted in a finding that a polyamine derivative having an anthraquinone skeleton showed a significant channel blocking activity (see Non-Patent Document 1 shown below).    Non-Patent Document 1: J. Pharm. Exp. Ther., 309:884-893